Positive electrode active material, positive electrode having the same and lithium secondary battery

This application is a divisional of U.S. patent application Ser. No. 18/203,027, filed May 29, 2023 (now U.S. Pat. No. 12,040,487), which is a divisional of U.S. patent application Ser. No. 16/802,551, filed Feb. 26, 2020 (now U.S. Pat. No. 11,721,808), which claims the benefit of U.S. Provisional Application 62/810,872 filed Feb. 26, 2019, the contents of which are herein incorporated by reference in their entirety.

The present invention relates to a carbon-deposited alkali metal oxyanion, as well as to a multi-step process for preparing same, and the use thereof of said carbon-deposited alkali metal oxyanion as cathode material in lithium secondary batteries.

Olivine-type LiFePOhas become an important cathode material for lithium ion batteries as a result of its superior capacity retention, thermal stability, nontoxicity and safety. But olivine LiFePOsuffers from significant disadvantages, such as low intrinsic and ionic conductivity. Coating with carbon can improve electrical conductivity, and poor lithium ion diffusion can be addressed by the synthesis of small particles.

In the specific case of a carbon-deposited lithium ferrous phosphate, referred to as C—LiFePO, several processes have been proposed to manufacture the material, either by pyrolysis of a carbon precursor on LiFePOor by simultaneous reaction of lithium, iron and POsources and a carbon precursor. For example, EP 1 049 182 A3 and US 2002/0195591 A1 describe solid-state thermal processes allowing synthesis of C—LiFePOincluding through the following reaction:

in which the carbon precursor is an organic material that forms a carbon deposit through pyrolysis while generating reducing gases that efficiently reduce the iron (III).

US 2007/0054187 A1 discloses the preparation of lithium metal phosphate LiMPOthrough the reaction of a Li-source, at least one M-source (M can be Fe, Mn, Co, Ni) and at least one PO-source under hydrothermal conditions at a temperature between 10° and 250° C. and at a pressure from 1 to 40 bar. The disclosed process comprises mixing LiMPOwith a carbon precursor, drying and calcining the obtained mixture, allowing synthesis of C-LiMPO.

The implementation of such processes at an industrial scale presents challenges as they involve a number of simultaneously occurring chemical, electrochemical, gas-phase, gas-solid reactions, sintering, and carbon deposition. The electrochemical properties of an alkali metal oxyanion electrode material having a carbon deposit are thus dependent on numerous parameters such as surface properties, wettability, surface area, porosity, particle size distribution, water-content, crystal structure, carbon deposit conductivity, as well as the raw materials chemistry, reactor feed rate, flow of gas, etc. All those properties are difficult to control in a very precise fashion during the reaction, which results in the obtaining of non-stoichiometric materials, the incompleteness of the reaction and the remaining of impurities in the obtained materials.

Problems therefore remain to find a simple and optimized process for making higher quality cathode materials for battery applications.

Therefore it is the object of the present invention to provide an alternative process for manufacturing carbon-deposited alkali metal oxyanion as cathode material, which shows similar if not better electrochemical performance than materials of the prior art when the carbon-deposited alkali metal oxyanion according to the present invention is used as active electrode material in lithium secondary batteries. Furthermore, it is the object of the present invention to provide a versatile process for the preparation of carbon-deposited alkali metal oxyanion comprising only a few synthesis steps, which can be conducted easily for manufacturing various grades of high-performance and cost-effective cathode materials. Moreover, at each steps, process allows efficient control and optimization of the precursors, impurities susceptible to reactions that are detrimental to battery operation, particle morphology and quality of carbon deposit.

The object is achieved by a multi-step process for the preparation of a carbon-deposited alkali metal oxyanion. In the specific case of a carbon-deposited lithium ferrous phosphate, referred to as C—LiFePO, said process preferably comprising the steps:

The invention further provides a carbon-deposited alkali metal oxyanion with a carbon deposit obtained by chemical vapor deposition process in presence of a gas-phase organic carbon source, and with a carbon deposit content according to the present invention less than 2.5 wt. %, preferably less than 2.0 wt. %, more preferably less than 1.6 wt. %, still more preferably less than 1.2 wt. %.

The invention further provides a carbon-deposited alkali metal oxyanion obtained by the process of the invention with a carbon deposit content less than 2.5 wt. %, and with a sulfur content of less than 80 ppm, preferably less than 60 ppm, more preferably less than 40 ppm, still more preferably less than 20 ppm.

The invention further provides a graphene-like carbon-deposited alkali metal oxyanion obtained by the process of the invention with 1 to 8 layers of said graphene-like carbon deposit.

The invention further provides a graphene-like carbon-deposited alkali metal oxyanion obtained by the process of the invention with 1 to 8 layers of said graphene-like carbon deposit, and with a sulfur content of less than 80 ppm, preferably less than 60 ppm, more preferably less than 40 ppm, still more preferably less than 20 ppm.

The invention further provides a carbon-deposited alkali metal oxyanion obtained by the process of the invention with a carbon deposit content less than 2.5 wt. %, and with alkali metal oxyanion primary particles having a median size to less than 500 nm, in a preferred embodiment less than 250 nm, in a more preferred embodiment less than 150 nm. In another preferred embodiment, primary particles have a median size comprised between 25 and 250 nm, preferably between 50 and 150 nm, more preferably between 70 and 130 nm.

The invention further provides a carbon-deposited alkali metal oxyanion obtained by the process of the invention with a carbon deposit content less than 2.5 wt. %, in the form of secondary agglomerates, preferably spherical, of primary particles with a median size between 50 and 250 nm, and with a BET value comprised between 3 and 13, preferably comprised between 5 and 11, more preferably between 5 and 9, still more preferably between 5 and 7 m/g. In another preferred embodiment, BET value is ≤13, preferably ≤11, more preferably ≤9, still more preferably ≤7 m/g.

The invention further provides a carbon-deposited alkali metal oxyanion obtained by the process of the invention with a carbon deposit content less than 2.5 wt. %, with a sulfur content of less than 80 ppm, preferably less than 60 ppm, more preferably less than 40 ppm, still more preferably less than 20 ppm, in the form of secondary agglomerates, preferably spherical, of primary particles with a median size between 50 and 250 nm, and with a BET value comprised between 3 and 13, preferably comprised between 5 and 11, more preferably between 5 and 9, still more preferably between 5 and 7 m/g. In another preferred embodiment, BET value is ≤13, preferably ≤11, more preferably ≤9, still more preferably ≤7 m/g.

The invention further provides a graphene-like carbon-deposited alkali metal oxyanion obtained by the process of the invention with 1 to 8 layers of said graphene-like carbon deposit, with a sulfur content of less than 80 ppm, preferably less than 60 ppm, more preferably less than 40 ppm, still more preferably less than 20 ppm, in the form of secondary agglomerates, preferably spherical, of primary particles with a median size between 50 and 250 nm, and with a BET value comprised between 3 and 13, preferably comprised between 5 and 11, more preferably between 5 and 9, still more preferably between 5 and 7 m/g. In another preferred embodiment, BET value is ≤13, preferably ≤11, more preferably ≤9, still more preferably ≤7 m/g.

The invention further provides the use of a carbon-deposited alkali metal oxyanion prepared by the process of the invention for the preparation of a cathode of a lithium secondary battery.

The invention further provides the use of a carbon-deposited alkali metal oxyanion obtained by the process of the invention with a carbon deposit content less than 2.5 wt. %, and with a sulfur content of less than 80 ppm, preferably less than 60 ppm, more preferably less than 40 ppm, still more preferably less than 20 ppm, for the preparation of a cathode of a lithium secondary battery with exceptional high-temperature electrochemical properties.

The invention further provides the use of a graphene-like carbon-deposited alkali metal oxyanion obtained by the process of the invention with 1 to 8 layers of said graphene-like carbon deposit, and with a sulfur content of less than 80 ppm, preferably less than 60 ppm, more preferably less than 40 ppm, still more preferably less than 20 ppm, for the preparation of a cathode of a lithium secondary battery with exceptional high-temperature electrochemical properties.

The invention further provides a lithium secondary battery comprising an anode, a cathode and an electrolyte, wherein the cathode comprises carbon-deposited alkali metal oxyanion manufactured by the process according to the present invention.

Despite a lower energy density than oxide cathode material, such as NMC and NCA, the need for a long-term perspective of advanced batteries with excellent safety, abuse tolerance electrochemistry, exceptionally efficiency over a wide operating temperature range, very long cycle life, low life weighted cost (price/kWh/cycle), outstanding high power/energy ratio, high-temperature performances, no use of cobalt critical raw material, implies carbon-deposited LiFePOwill remain in the future a key and cost-effective electrode material for fast growing market like drop-in replacement for lead-acid batteries, SLI batteries, mild hybrids 48 V automotive functions, electric vehicles market, large scale electricity storage, electric buses and trucks, automatic guide vehicles, forklifts, hybrid and fully electric train, or hybrid and fully electric marine battery systems (ferries, large vessels with MWh-size batteries).

For specific case of electric vehicles, intrinsic safety of battery using carbon-deposited LiFePOallows to develop advanced generation of battery pack with less safety component, cooling and packaging material, especially with innovative cell-to-pack or blade battery technology. Moreover, the rapid growth of EV market in the last years has resulted in continuous improvement in EV energy efficiency (lower Wh/km from optimization of electric motor, power electronic, BMS, tire, heat pump heater, hardware, and software), making batteries using advanced carbon-deposited LiFePOa viable solution for cost-effective EV with range large enough to fulfill needs of a substantial part of end users.

The inventors have discovered that to ensure those excellent performances in harshest conditions (high-temperature cycling and storage), synthesis of carbon-deposited alkali metal oxyanion, like C—LiFePO, obtained with a multi-step process combining precursors sintering, water-based nanomilling and chemical vapor deposition of carbon deposit, it is surprisingly essential to control impurities and side reaction to unexpectedly low level at each step.

In one non-limiting embodiment, alkali metal oxyanion is a compound corresponding to the general nominal formula AM(XO), wherein: A represents Li, alone or partially replaced by at most 20% as atoms of Na and/or K; M comprise at least 50% at. of Fe(II) or Mn(II) or mixture thereof; and XOrepresents PO, alone or partially replaced by at most 30 mol % of at least one group chosen from SOand SiO; a, m, and x being such that 0<a≤8, 1≤m≤3, 0<x≤3, and wherein M, X, a, m and x are selected as to maintain electroneutrality of said compound.

In another non-limiting embodiment, alkali metal oxyanion is a compound corresponding to the general nominal formula AM(XO), wherein: A represents Li, alone or partially replaced by at most 20% as atoms of Na and/or K; M comprise at least 95% at. of Fe(II) or Mn(II) or mixture thereof; and XOrepresents PO, alone or partially replaced by at most 30 mol % of at least one group chosen from SOand SiO; a, m, and x being such that 0<a≤8, 1≤m≤3, 0<x≤3, and wherein M, X, a, m and x are selected as to maintain electroneutrality of said compound.

In another non-limiting embodiment, alkali metal oxyanion is a compound corresponding to the general nominal formula AM(XO), wherein: A represents Li, alone or partially replaced by at most 20% as atoms of Na and/or K; M is selected from the group consisting of Fe(II), Mn(II), or mixture thereof, alone or partially replaced by at most 5% as atoms of one or more metals comprising Ni, or Co, or aliovalent or isovalent metals selected from the group consisting of Mg, Mo, Nb, Ti, Al, Ta, Ge, La, In, Y, Yb, Cu, Sm, Sn, Pb, Ag, V, Ce, Hf, Cr, Zr, Bi, Zn, Ca, Cd, Ru. Ga, Sr, Ba, B and W; and XOrepresents PO, alone or partially replaced by at most 30 mol % of at least one group chosen from SOand SiO; a, m, and x being such that 0<a≤8, 1≤m≤3, 0<x≤3, and wherein M, X, a, m and x are selected as to maintain electroneutrality of said compound.

In another non-limiting embodiment, alkali metal oxyanion is a compound which has an olivine structure corresponding to the general nominal formula LiMPO, wherein M comprises at least 95% at., preferably at least 97% at., most preferably at least 99% at. of Fe(II), or Mn(II), or mixture thereof, metal balance is optionally one or more other metals, comprising Ni, or Co, or aliovalent or isovalent metals selected from the group consisting of Mg, Mo, Nb, Ti, Al, Ta, Ge, La, In, Y, Yb, Cu, Sm, Sn, Pb, Ag, V, Ce, Hf, Cr, Zr, Bi, Zn, Ca, Cd, Ru, Ga, Sr, Ba, B and W.

In another non-limiting embodiment, alkali metal oxyanion is a compound which has an olivine structure corresponding to the general nominal formula LiMPO, wherein M comprises at least 60% at. of Mn(II) and at least 20% at. of Fe(II), alone or partially replaced by at most 5% as atoms of one or more other metals, comprising Ni, or Co, or aliovalent or isovalent metals selected from the group consisting of Mg, Mo, Nb, Ti, Al, Ta, Ge, La, In, Y, Yb, Cu, Sm, Sn, Pb, Ag, V, Ce, Hf, Cr, Zr, Bi, Zn, Ca, Cd, Ru, Ga, Sr, Ba, B and W.

In another non-limiting embodiment, alkali metal oxyanion is a compound which has an olivine structure corresponding to the general nominal formula LiMPO, wherein M comprises at least 97% at., preferably at least 98% at., most preferably at least 99% at. of Fe(II), metal balance is optionally one or more other metals, comprising Ni, or Co, or aliovalent or isovalent metals selected from the group consisting of Mg, Mo, Nb, Ti, Al, Ta, Ge, La, In, Y, Yb, Cu, Sm, Sn, Pb, Ag, V, Ce, Hf, Cr, Zr, Bi, Zn, Ca, Cd, Ru, Ga, Sr, Ba, B and W.

In another non-limiting embodiment, alkali metal oxyanion is a compound which has an olivine structure corresponding to the general nominal formula LiFePO.

By “general nominal formula” one means that the stoichiometry of the material of the invention can vary by a few percent from stoichiometry due to substitution or other defects present in the structure, including anti-sites structural defects such as, without any limitation, cation disorder between iron and lithium in LiFePOcrystal, see for example Maier et al. [Defect Chemistry of LiFePO, Journal of the Electrochemical Society, 155, 4, A339-A344, 2008] and Nazar et al. [Proof of Supervalent Doping in Olivine LiFePO, Chemistry of Materials, 2008, 20 (20), 6313-6315].

a) Sintering of Precursors Step

Olivine structure alkali metal oxyanion to be synthesized is preferably LiMPO, wherein M comprises at least 95% at., preferably at least 97% at., most preferably at least 99% at. of Fe(II), or Mn(II), or mixture thereof, metal balance (referred as “additional metal”) is optionally one or more other metals.

In a non-limiting embodiment, additional metal is optionally one or more other metals comprising Ni, or Co, or aliovalent or isovalent metals selected from the group consisting of Mg, Mo, Nb, Ti, Al, Ta, Ge, La, In, Y, Yb, Cu, Sm, Sn, Pb, Ag, V, Ce, Hf, Cr, Zr, Bi, Zn, Ca, Cd, Ru, Ga, Sr, Ba, B and W.

Starting material compounds for the synthesis of LiMPO, comprising at least one lithium source, at least one iron and/or manganese metal source, optionally at least one additional metal source, at least one phosphate source, and at least one organic carbon source are subjected to at least one mixing, preferably milling step, performed as a dry or wet process. The sources can be in the form of compounds having more than one source element.

Wet milling is performed in presence of a liquid acting as fluid carrier, for example water or an organic solvent, and mixture thereof. Preferably fluid carrier is chosen among water or alcohol, and mixture thereof. In a preferred embodiment, alcohol is selected among aliphatic alcohols having 1 to 10 carbon atoms like methanol, ethanol, propanols, for example n-propanol or iso-propanol, butanols, for example n-butanol or iso-butanol, and mixture thereof.

In a non-limiting embodiment, water is preferably deionized.

In a non-limiting embodiment, wet milling is performed in alcohol.

In a non-limiting embodiment, alcohol contains less than 2 wt. % of water, preferably less than 1 wt. %, more preferably less than 0.5 wt. %.

In a non-limiting embodiment, a degasification of fluid carrier can be performed prior wet milling step by any method well known to a person of ordinary skill in the art.

During the development of the process, inventors realized that when milling is performed without fluid carrier as a dry milling, process might be less efficient in some implementation, particularly at large scale. Moreover, dry milling may in some implementation generate local overheating of the precursors with potential undesired impurities formation, contrarily to wet milling wherein fluid carrier can contribute to evacuate heat. It is why in a non-limiting mode of operation, milling is preferably performed as a wet milling.

Any known dry or wet milling technique can be employed, such as, but without being limited to, ball or bead mills, planetary ball mills, colloid mills, vibration mills, mixer mills, rotor-stator mills, shaker ball mills, disc mills, sand mills, pebble mills, jar mills, ultrasonic and ultrasonic assisted mills, submersible basket mills, basket sand mills, high-kinetic rotor ball mills, stirred bead mills, attritors, and equivalent milling equipment. Preferred dry or wet milling is ball or bead milling, more preferably high-energy ball or bead milling.

Available laboratory and industrial equipment can be used to perform the at least one dry and/or wet high-energy ball or bead milling step. Suitable high-energy milling equipment is available from Union Process (Akron, Ohio 44313), Zoz GmbH (Weeden, Germany). Netzsch-Feinmahltechnik GmbH (Seib, Germany), Retsch GmbH (Haan, Germany), Fritsch GmbH (Idar-Oberstein, Germany), Buhler AG (Uzwil, Switzerland), SPEX SamplePrep (Metuchen. N.J. 08840), Shandong Longxing Chemical Machinery Group Co. (Yantai, Shandong, China) among other possible suppliers. Specific examples of such suitable high-energy milling equipment include, but without being limited thereto, the Attritor® 1-S having 7.6 L process vessel, the Attritor® SD-30 having 200 L process vessel, and the Attritor® SD-50 having 300 L process vessel (Union process), the Simoloyer CM08 (Zoz), the MasterMill 30 submersible basket mill (Netzsch), the Centex™ T3 agitated bead mill (Buhler), the LMJ-37 basket sand mill (Shandong Longxing Chemical Machinery Group), and the SPEX 8000D Mixer/Mill (SPEX SamplePrep). The person skilled in the art will be able to select suitable equipment to perform wet and/or dry milling without departing from the spirit of the invention.

In one non-limiting implementation, duration time of the milling step of the invention is between 5 minutes to 4 hours, preferably between 10 minutes and 2 hours, more preferably between 15 minutes and 1 hour. In another non-limiting implementation, milling step is performed in less than 2 hours, preferably in less than 1 hour, more preferably in less than 30 mn, still more preferably in less than 15 mn.

After milling, and optional separation step when milling is performed as wet milling (e.g. without any limitation by filtration, centrifugation, evaporation, drying, agitating media drying, filter press, or spray drying), milled material is subjected to at least one heat treatment.

In a non-limiting mode of operation, optionally at least one compacting process step can be added, which can take place as mechanical compaction e.g. by means of a roll compactor or a tablet press, but can also take place as rolling, build-up or granulation or by means of any other technical method appearing suitable for the purpose to a person skilled in the art.

In a broad non-limiting implementation, the heating of the milled material is performed in a chemical reactor allowing controlling the atmosphere and/or the heat treatment temperature.

In one non-limiting embodiment the heating of the milled material is performed at a temperature between 30° and 800° C., in a preferred embodiment between 50° and 700° C., in a more preferred embodiment between 55° and 650° C., in a still more preferred embodiment between 575 and 625° C.